Real-time interactivity is provided across a shared multiple-participant three-dimensional (3D) virtual-reality environment on the World Wide Web (WWW), with the purpose of allowing a plurality of users to participate in a 3D virtual-reality world where the participants can share information and interact with each other substantially in real time. Through the use of a Client-Information Manager Program (CIMP) module, which is connected via a Common Gateway Interface (CGI) module to the WWW server, each user is able to interactively communicate with any of the other users participating together in the same 3D virtual-reality world. The shared multiple-participant 3D virtual-reality environment utilizes modified Protocol Data Unit (PDU) formats based on the Distributive tive Interactive Simulation (DIS) protocol for data communication among the WWW server and the various client sites. Moreover, the shared multiple-participant 3D virtual-reality environment utilizes a Dead Reckoning (DR) method with a predetermined optimal mal DR threshold to help reduce the rate of Object-State PDUs that are generated in response sponse to changes in each user's avatar state, so that avatar state updates can be more quickly transmitted to all the other client sites participating in the same 3D virtual-reality world.